Damgard Jurik Encryption for eVoting - Not yet working example that 'tries' to use the great SCAPI lib

DamgardJurikTest.java

package org.doogie;

import edu.biu.scapi.midLayer.asymmetricCrypto.encryption.DJKeyGenParameterSpec;
import edu.biu.scapi.midLayer.asymmetricCrypto.encryption.DamgardJurikEnc;
import edu.biu.scapi.midLayer.asymmetricCrypto.encryption.ScDamgardJurikEnc;
import edu.biu.scapi.midLayer.asymmetricCrypto.keys.ScDamgardJurikPublicKey;
import edu.biu.scapi.midLayer.ciphertext.AsymmetricCiphertext;
import edu.biu.scapi.midLayer.plaintext.BigIntegerPlainText;

import java.math.BigInteger;
import java.security.InvalidKeyException;
import java.security.KeyException;
import java.security.KeyPair;
import java.security.PublicKey;
import java.security.spec.InvalidParameterSpecException;

/**
 * Example for casting votes that are encrypted with the  DamgardJuric Encryption Scheme
 * This is just my try of using this lib. I barely understand what I am doing here :-)
 */
public class DamgardJurikTest {

  public static void main(String[] args)  {
    try {
      DamgardJurikTest dj = new DamgardJurikTest();
    } catch (Exception e) {
      System.out.println("FATAL ERROR: "+e);
      e.printStackTrace();
    }
  }

  public DamgardJurikTest() throws Exception {
    PublicKey tallyPublicKey = setupTally();
    DamgardJurikEnc voteEncryptor = setupVoter(tallyPublicKey);
    castVote(voteEncryptor, BigInteger.ONE);    // 0/1 == vote for or against a candidate
    doTally();
  }

  /**
   * Setup a tally board that can receive (encrypted) votes.
   * @return The publicKey of this tally board, that voters need to encrypt their personal votes
   * @throws InvalidParameterSpecException
   */
  public PublicKey setupTally() throws InvalidParameterSpecException {
    log("setupTally...");
    //Create a DamgardJurik encryption object.
    DamgardJurikEnc tallyEnc = new ScDamgardJurikEnc();

    //Generate a keyPair using the DamgardJurik object.
    KeyPair tallyKeyPair = null;
    try {
      tallyKeyPair = tallyEnc.generateKey(new DJKeyGenParameterSpec(128, 40));
    } catch (InvalidParameterSpecException e) {
      System.out.println("Cannot generate key for Tally " + e);
      throw e;
    }
    
    //Publish your public key.
    BigInteger modulus = ((ScDamgardJurikPublicKey)tallyKeyPair.getPublic()).getModulus();
    log("tally public key = "+modulus);
    return tallyKeyPair.getPublic();
  }

  /**
   * setup a voter that can later cast a vote
   * @param tallyPublicKey the publicKey of the tally board that we will send our (encrypted) vote to. We will encrypt with this public key.
   * @throws InvalidParameterSpecException
   * @throws InvalidKeyException
   */
  public DamgardJurikEnc setupVoter(PublicKey tallyPublicKey) throws InvalidParameterSpecException, InvalidKeyException {
    BigInteger modulus = ((ScDamgardJurikPublicKey)tallyPublicKey).getModulus();
    log("setupVoter(tallyPublicKey="+modulus+")");

    //Create a DamgardJurik encryption object.
    DamgardJurikEnc voteEnc = new ScDamgardJurikEnc();

    //Generate a keyPair using the DamgardJurik object.
    KeyPair votersKeyPair = null;
    try {
      votersKeyPair = voteEnc.generateKey(new DJKeyGenParameterSpec(128, 40));
    } catch (InvalidParameterSpecException e) {
      System.out.println("Cannot generate key for Voter " + e);
      throw e;
    }

    //Publish your public key.
    //publish(pair.getPublic());          // why is that necessary?

    //Set private key and party2's public key:
    try {
      voteEnc.setKey(tallyPublicKey, votersKeyPair.getPrivate());
    } catch (InvalidKeyException e) {
      System.out.println("Cannot use public key of authority. InvalidKeyException: " + e);
      throw e;
    }

    return voteEnc;
  }

  public void castVote(DamgardJurikEnc voteEncryptor, BigInteger vote) {
    log("castVote(vote='"+vote+"')");
    //Get the BigInteger value to encrypt, create a BigIntegerPlaintext with it and encrypt the plaintext.
    BigIntegerPlainText plaintext = new BigIntegerPlainText(vote);  //Remark: There is also a constructor for String.  Can I also encrypt Strings?
    log("Plaintext = "+plaintext);
    AsymmetricCiphertext cipher = voteEncryptor.encrypt(plaintext);
    log("Encrypted vote = "+cipher);

    //Send cipher and keys to the receiver.

    log("============");

    try {
      BigIntegerPlainText decrypted_plaintext = (BigIntegerPlainText) voteEncryptor.decrypt(cipher);
      log("Decrypted "+decrypted_plaintext);
      //String decr_vote = new String(decrypted_plaintext.getX().toByteArray());
      //log("Decrypted vote = "+decr_vote);
    } catch (KeyException e) {
      System.out.println("ERROR: Cannot decrypt plaintext "+e);
      e.printStackTrace();
    }
  }

  /** sum up the (encrypted) votes */
  public void doTally() {
    log("doTally ... <not implemented yet>");
    //TODO:
  }


  /**
   * very simple log output
   * @param msg any string message
   */
  public static void log(String msg) {
    System.out.println(msg);
  }
}